Pay-as-you-go or pay-per-use business models have been used in many areas of commerce, from cellular telephones to commercial laundromats. In developing a pay-as-you go business, a provider, for example, a cellular telephone provider, offers the use of hardware (a cellular telephone) at a lower-than-market cost in exchange for a commitment to remain a subscriber to their network for a period of time. In this specific example, the customer receives a cellular phone for little or no money in exchange for signing a contract to become a subscriber for a given period of time. Over the course of the contract, the service provider recovers the cost of the hardware by charging the consumer for using the cellular phone.
In the case of the cellular telephone, all charges are billed, mediated, and accrued on the network side. Even a pre-paid user account has value, in terms of minutes or text messages, stored on the network and a local SIM card for identifying the phone/account to the network. Because the phone is essentially useless unless connected to the network, the model works.
However, unlike a cellular telephone, a pay-per-use computer may have substantial value to a user even though only occasionally connected to a network. Therefore, the computer must be able to meter and monitor its own operation with only infrequent access to a network host. While potential lack of access places a significant security burden on the computer to fairly meter usage, it also requires special consideration at the network end. Because a network server and the pay-per-use computer may only have occasional, and sometimes brief contact with each other, the network server must be able to respond quickly and correctly to requests from the computer. Likewise, requests from customer service or a repair facility must be coordinated so that correct information is available in a timely manner. Underlying all communication and metered-use activity is a security core based on cryptographic principals which brings its own requirements.